This invention relates to an apparatus for in-line surface finishing elongate cylindrical stock, for example, stainless steel tubing, and a method for in-line surface finishing of cylindrical stock such as stainless steel tubing. Use of the term "in-line" is used in this application to mean that the scratch pattern of the surface finish applied to the stock extends substantially parallel to, or linearly along, the longitudinal axis of the stock, in contrast to prior art radial finishing techniques wherein the scratch pattern extends generally radially around the surface of the stock substantially perpendicular to the longitudinal axis of the stock.
The invention will be described in this application with respect to in-line buffing the surface of stainless steel tubing to achieve a chrome-bright finish. Tubing finished in this manner has numerous mechanical and ornamental applications, including railing and ladders for boats, exterior vehicle accessories, and metal furniture structural pieces such as legs and arms. However, the principles of the invention have application in applying differing types of surface finishes to other types of tubing, pipe and solid cylindrical stock.
The apparatus and process described comes near the end of a number of other prior art processes, the major ones being described briefly below.
In general, coiled stainless steel sheet between 18 inches and 60 inches wide and 5,000 feet long is slit into a strip which is as wide as the circumference of the tubing to be formed. For example, tubing having an O.D. of one inch will be slit into a strip 3.1416 inches wide. The strip is rolled back into a coil and taken to a tube mill. The tubing is formed by traversing the strip in a continuous process through a series of forming rollers. The initial stage is referred to as the "breakdown" stage, where the opposing edges are turned upwardly.
The strip is then passed to a "fin" section, where the opposing edges are gradually and progressively curved upwardly towards each other until the strip has been formed into a closed cylindrical tube with the opposing edges aligned with each other.
The tube is passed through a welding machine where the two opposing edges are continuously welded to each other. The welded tube then passes through a grinder where the weld is ground flush with the adjacent walls of the tube. The tube is then passed through a precision-sizing section where a series of precisely sized and aligned sizing rollers shape the tubing to its final size and cylindrical shape.
The tubing is then cut to a predetermined manageable length, for example, 30 feet, for further processing.
In some prior art processes, the tubing is then polished. "Polishing" is a term of art which means using progressively finer-grit sandpaper to put an initial smooth finish on the exterior surface of the tubing. The sandpaper is applied to the tubing as the tubing is rotated. Thus, a radial finish is applied to the tubing during this process. The scratch pattern formed during this process extends radially around the outer circumferential surface of the tubing and are quite easily seen when light is reflected off of the tube. In relative terms, polishing applies a crude finish which is sufficient for some mechanical applications, but not for other mechanical applications, particularly when the tubing also serves an ornamental function. Tubing which is radially polished in the manner described above must also be radially buffed.
Prior art buffing is also carried out radially. The tubing is fed into a buffing machine while being rotated about its longitudinal axis. Large buffing wheels rotating about axes which are parallel to the longitudinal axis of the tubing are pressed against the outer circumferential surface of the tubing as it extends down the length of the machine. These wheels generally rotate in the range of 1,800-2,000 rpm. A typical prior art configuration would include four buffing wheels in axial alignment with each other and spaced approximately 3 feet apart. The wheels are generally either fabricated of sisal or cotton cloth or a combination of both, with all or predominately sisal wheels being used on the infeed end of the machine and the all or predominately cotton cloth wheels being used near the outfeed end. The fourth wheel is generally all cotton and is referred to as a "fluffy wheel." Various types of buffing compounds are periodically applied to the wheels during operation, and it is the buffing compound and not the wheel from which the material is made which actually performs the buffing process. The sisal or cotton acts primarily as a carrier for the buffing compound.
Friction creates a temperature at the outfeed position of approximately 400.degree. F. An advantage of the prior art radial buffing process is that the tubing can be very evenly buffed on all surfaces while the tubing is supported. Thus, warping of the tubing is minimal.
When properly carried out, this buffing process applies a final chrome-bright finish to the tubing resembling a chrome-plated finish. However, light striking the tubing at particular angles reveals the radial scratch pattern necessarily applied during the process. This scratch pattern gives the tubing a "look" which many end users find less than ideal, and which can create a distinct contrast with adjacent, short lengths of tubing which have been hand buffed, or are chrome-plated.
Prior efforts have been made by applicant and others to buff stainless steel tubing linearly or "in-line" with the longitudinal axis of the tubing using wheels such as used for radial buffing. To applicant's knowledge all such efforts have failed, and there is presently no known commercial manufacture of stainless steel tubing or other cylindrical stock wherein a buffed finish is applied "in-line."
The apparatus and method disclosed in this application buffs stainless steel tubing "in-line" at commercial speeds to a chrome bright finish which exhibits a highly desirable ornamental appearance.